push: more precise failure check on subrepo push

This will let us distinguish between nothing to push and push failed

mercurial/commands.py

@@ -4419,7 +4419,7 b' def push(ui, repo, dest=None, **opts):'
         c = repo['']
         subs = c.substate # only repos that are committed
         for s in sorted(subs):
-            if not c.sub(s).push(opts):
+            if c.sub(s).push(opts) == 0:
                 return False
     finally:
         del repo._subtoppath

mercurial/subrepo.py

@@ -528,7 +528,7 b' class hgsubrepo(abstractsubrepo):'
         c = self._repo['']
         subs = c.substate # only repos that are committed
         for s in sorted(subs):
-            if not c.sub(s).push(opts):
+            if c.sub(s).push(opts) == 0:
                 return False
 
         dsturl = _abssource(self._repo, True)